The present invention relates to the field of microwave technology, and more specifically to an arrangement for broadband transition between a microstrip and a waveguide.
Microwaves are electromagnetic waves that have very short wavelengths whose frequencies are usually defined as lying between 1 and 100 GHz (in other words, wavelengths in the range of 0.3 to 30 cm). They are utilized in different technical applications, for instance in microwave ovens, radar and telecommunications. A common feature of the two latter applications is that microwaves are often transmitted and received by one or more antennas.
Microwaves are often modulated and otherwise processed in special circuits, so-called monolithic microwave integrated circuits (MMIC). These circuits are normally disposed on or in substrates with microstrip lines for internal transmission. The substrates are similar to typical circuit boards although adapted in different ways, particularly for microwaves. For instance, the microstrip lines are dimensioned for the frequency or frequencies for which they are intended. The transmission of microwaves between different equipment components is often effected in waveguides. A waveguide is essentially a tube between whose conductive walls the microwaves can be said to bounce forwards in the direction of the tube. The waveguides have several good microwave transmission properties, such as low transmission losses, and allow filters to be readily incorporated therein, among other things.
Some type of junction is required in order to enable microwaves to be transferred between substrate and waveguide. Since the invention relates to such a junction between a microstrip and a waveguide, it is this type of junction that is described in the following.
Earlier known junctions between microstrip and waveguide can be described roughly as follows. A narrow substrate tongue is inserted sideways into one end of the waveguide. The end of the tongue carries a so-called pad, which consists of an often square substrate coating, which transfers signals between the microstrip and the waveguide. In order to obtain the best possible junction, it is important to adapt the pad to those frequencies at which it shall operate. The parameters that determine primarily the effectiveness of such adaptation are the length and width of the pad and the extent to which it enters the waveguide.
The aforedescribed junction normally has a narrow band but is well matched. The bandwidth of the junction is normally about 10-15%, i.e. the junction functions for a frequency band whose width is 10-15% of the frequency for which the junction is designed. The frequency band spreads centrally around this frequency.
One problem occurring with a narrowband junction is that it becomes sensitive to mechanical tolerances of the various components and also to mounting tolerances. This often requires the junction to be trimmed in order for it to function effectively. In the worst case, this sensitivity may mean that the junction will not function at all at the contemplated frequency.
The present invention addresses the problem of improving the effectiveness of microstrip-waveguide junctions.
One object of the present invention is therefore to provide a microstrip-waveguide junction that has a wider band than earlier known junctions.
Another object is to provide a microstrip-waveguide junction that will not need to be trimmed.
In brief, the invention is generally characterised in that the pad carried by the tongue inserted into the waveguide includes two signal transferring parts. These parts are situated on the upper side and lower side of the tongue respectively. The underside of the tongue is in electric contact with the upper side thereof, so that signals can be sent to and received from the microstrip. The two sides of the tongue are therewith designed for different, often mutually adjacent frequencies, so that they can cover a broader frequency band than a simple pad. Such a junction will also be less sensitive to different tolerances.
The invention will now be described in more detail with reference to preferred exemplifying embodiments thereof and also with reference to the accompanying drawings.